Do not #define keywords.

interpreter/cling/include/cling/Interpreter/Exception.h

@@ -12,8 +12,12 @@
 
 #include <exception>
 
-#if defined(_MSC_VER) && (_MSC_VER < 1900) && !defined(noexcept)
-  #define noexcept
+#ifndef CLING_NOEXCEPT
+# if defined(_MSC_VER) && (_MSC_VER < 1900)
+#  define CLING_NOEXCEPT
+# else
+#  define CLING_NOEXCEPT noexcept
+# endif
 #endif
 
 namespace clang {
@@ -27,9 +31,9 @@ namespace cling {
   ///
   class InterpreterException : public std::exception {
   public:
-    virtual ~InterpreterException() noexcept;
+    virtual ~InterpreterException() CLING_NOEXCEPT;
 
-    virtual const char* what() const noexcept;
+    virtual const char* what() const CLING_NOEXCEPT;
     virtual void diagnose() const {}
   };
 
@@ -46,9 +50,9 @@ namespace cling {
     DerefType m_Type;
   public:
     InvalidDerefException(clang::Sema* S, clang::Expr* E, DerefType type);
-    virtual ~InvalidDerefException() noexcept;
+    virtual ~InvalidDerefException() CLING_NOEXCEPT;
 
-    const char* what() const noexcept override;
+    const char* what() const CLING_NOEXCEPT override;
     void diagnose() const override;
   };
 } // end namespace cling

interpreter/cling/lib/Interpreter/DeclUnloader.h

@@ -14,8 +14,12 @@
 
 #include "clang/AST/DeclVisitor.h"
 
-#if defined(_MSC_VER) && (_MSC_VER < 1900) && !defined(constexpr)
-  #define constexpr const
+#ifndef CLING_CONSTEXPR
+# if defined(_MSC_VER) && (_MSC_VER < 1900)
+#  define CLING_CONSTEXPR const
+# else
+#  define CLING_CONSTEXPR constexpr
+# endif
 #endif
 
 namespace clang {
@@ -256,7 +260,7 @@ namespace clang {
     ///
     void CollectFilesToUncache(SourceLocation Loc);
 
-    constexpr static bool isDefinition(void*) { return false; }
+    CLING_CONSTEXPR static bool isDefinition(void*) { return false; }
     static bool isDefinition(TagDecl* R);
 
     static void resetDefinitionData(void*) {